← Back to Sessions

The Effect of Fore-Arc Deformation on Shallow Earthquake Rupture Behavior in the Cascadia Subduction Zone

Session: Earthquake Science, Hazards and Policy in Cascadia II

Type: Oral

Date: 4/20/2021

Presentation Time: 05:30 PM Pacific

Description: 

Observational studies find along-strike variations in the geometrical properties of the Cascadia subduction zone (CSZ) megathrust. The megathrust of offshore Oregon is steeper and rougher than the megathrust of the offshore Washington region. Additionally, active source seismic surveys reveal significant along-strike differences in both the orientation of splay faults and sediment consolidation within the fore-arc of the CSZ. To investigate how the difference in the geometrical properties of megathrust and the difference in the fore-arc deformation style may affect the seismic and tsunami hazard during a future megathrust earthquake, we perform 2D dynamic earthquake rupture simulations on different realizations of a fault system that incorporate fore-arc properties representative of offshore Oregon and Washington. We find that both the shallow up-dip rupture behavior and the geometry of the fault affect the ground motions. The peak ground velocity (PGV) is larger for the Oregon models as compared to the Washington model at near-fault distances (due to larger fault slip in the shallow region) while it is lower at far-fault distances (since Oregon megathrust is steeper). Furthermore, we find that splay faults are activated irrespective of their orientation, but that slip is larger on the faults with seaward orientations. This amplifies seafloor uplift above these splays. Meanwhile, the difference in the consolidation of the CSZ sediments does not significantly influence seafloor uplift. If anelastic deformation of the material is allowed, uplift above the splay faults increases, and the difference between the uplift above the splay faults of the Washington and Oregon model is reduced. Our results suggest that the existence of splay faults, and their orientation can be a first-order control in the tsunami hazard model for the region as the predicted tsunami heights are significantly larger for Oregon than for Washington.

Presenting Author: Khurram Aslam

Student Presenter: No

Authors